The present invention relates to a vibration damping device which suppresses vibrations of a structure.
Conventionally, a vibration damping device which suppresses vibrations of a structure (hereinafter also simply referred to as “damping device”) is classified into a viscosity-type damping device, a friction-type damping device, and a plastic-type damping device.
A viscosity-type damping device is, for example, an oil damper, a dash pot or the like and, in general, a damping force of the damping device is in proportion to a speed (frequency) of vibrations of a structure (natural vibrations). Accordingly, in the viscosity-type damping device, the longer a period of vibrations of a structure, the more difficult the acquisition of a sufficient damping force becomes. In view of the above, in the viscosity-type damping device, when a damping device is applied to a long-period structure having a relatively long period of vibrations, for acquiring a desired damping force, in comparison to a case where a damping device is applied to a short-period structure having a relatively short period of vibrations, there exists a drawback that it is necessary to make the damping device large-sized or to impart high permeance to the damping device to acquire a desired damping force. Large-sizing of the device and the acquisition of high performance pushes up the installation cost.
In a friction-type damping device, in general, the magnitude of a fractional force which acts as a damping force is set to a fixed value irrelevant to the displacement by the vibrations of a structure. Accordingly, the friction-type damping device has a drawback that when the amplitude of vibrations is relatively small, the damping device cannot sufficiently exhibit the function thereof due to the seizure between slide surfaces which generate a frictional force, while when the amplitude of vibrations is relatively large, an equivalent viscous damping coefficient decreases as the amplitude increases. Here, the equivalent viscous damping coefficient is obtained by converting the damping performance of the damping device into the viscous damping coefficient of the viscosity-type damping device, and is a numerical value which becomes an index for damping performance of the damping device in the form of a single body.
The plastic-type damping device, in general, possesses both a kinetic characteristic of an elastic body and a kinetic characteristic of a plastic body. Accordingly, the plastic-type damping device has a drawback that when the vibrations are of small amplitude, the damping device functions as an elastic body so that an equivalent viscous damping coefficient is small, while when the vibrations are of large amplitude, the damping device functions as a complete elastic body so that the equivalent viscous damping coefficient decreases along with the increase of amplitude.
In view of the drawbacks which the above-mentioned respective damping devices have, the ideal damping device is a damping device where a damping effect is maintained even when a cycle of a natural vibration mode of a structure is lengthened, and the equivalent viscous damping coefficient does not decrease along with the increase of amplitude. With the use of such a damping device, it is thought that the vibration energies ranging from vibration energy of small amplitude to vibration energy of large amplitude can be absorbed efficiently for various and disparate structures regardless of a length of a cycle of the vibrations of a structure.
Here, attention is paid to a friction-type damping device where the mechanism for generating a damping force is relatively simple. In the friction-type damping device, it is thought that the influence which the lengthening of a period of vibrations exerts on a damping effect is relatively small so that the magnitude of a frictional force changes along with the displacement generated by the vibrations of a structure whereby the drawback attributed to the above-mentioned magnitude of the amplitude is overcome thus realizing the acquisition of an ideal damping device. As techniques relating to the friction-type damping device, there are techniques disclosed in JP-A-2007-177864 and JP-A-2005-201287.
JP-A-2007-177864 discloses the constitution having a mechanism which increases or decreases the damping of an earthquake motion corresponding to the magnitude of amplitude of the earthquake motion. JP-A-2005-201287 discloses the constitution where a plurality of supports which sandwich balls by upper and lower discs, guide rods which guide the movement of upper and lower plates and the like are provided between the upper and lower plates which are relatively movable in the horizontal direction, and a frictional force is increased corresponding to a moving amount of the upper and lower plates in the horizontal direction.
In the technique disclosed in JP-A-2007-177864, the mechanism which increases or decreases the damping of an earthquake motion corresponding to the magnitude of amplitude of the earthquake motion is a link mechanism constituted of a plurality of links, while in the technique disclosed in JP-A-2005-201287, the mechanism which is the combination of the upper and lower discs, the balls, the guide rods and the like is adopted. Accordingly, in both techniques disclosed in JP-A-2007-177864 and JP-A-2005-201287, the mechanism for generating a damping force by a frictional force is complicated and requires a large number of parts so that both techniques are not suitable for practical use.